The present invention relates generally to semiconductor packaging and more particularly to improved leadless leadframe based packaging.
A leadless leadframe package (LLP) is a relatively new integrated circuit package design that contemplates the use of a metal (typically copper) leadframe type substrate structure in the formation of the conductive elements of a package. As illustrated in FIG. 1, in typical leadless leadframe packages, a copper leadframe strip or panel 101 is patterned (typically by stamping or etching) to define a plurality of arrays 103 of chip substrate features 105. Each chip substrate feature 105 includes a die attach pad 107 and a plurality of contacts 109 disposed about their associated die attach pad 107. Very fine tie bars 111 are used to support the die attach pads 107 and contacts 109.
During assembly, dice are attached to the respective die attach pads and conventional wire bonding is used to electrically couple bond pads on each die to their associated contacts 109 on the leadframe strip 101. After the wire bonding, a plastic cap is molded over the top surface of the each array 103 of wire bonded dice. The wire bonded units are then singulated and tested using conventional sawing and testing techniques. During singulation, the tie bars 111 are cut and therefore the only materials holding the contacts 109 in place is the molding material. The resulting packaged chip can then be surface mounted on a printed circuit board or other substrate using conventional techniques.
Although leadless leadframe packaging has proven to be a cost-effective packaging arrangement, there are continuing efforts to further reduce the costs associated with packaging. Most existing leadless leadframe designs have only one or two rows of contacts 109. Accordingly additional and improved leadless leadframe designs that are particularly well suited for use in relatively high pin count devices would be desirable.
To achieve the foregoing and other objects and in accordance with the purpose of the present invention, a packaging arrangement is described that utilizes a conductive panel (such as a leadless leadframe) as its base. The conductive panel has a matrix of device areas that each include a plurality of rows of contacts that are located outside of a die area. Tie bars provide support for the various contacts. Some of the tie bars are arranged to extend between adjacent contacts in the same row and some of the tie bars are arranged to extend diagonally between associated contacts in adjacent rows that are not adjacent one another. With the described arrangement, during packaging, the tie bars can be severed by cutting along lines (e.g. saw streets) that run adjacent the rows after a molding operation.
In some preferred embodiments, the contacts in each device area are arranged at least three adjacent rows deep. The tie bars may have a thickness that is less than the thickness of the contacts, as for example about half the thickness of the contacts to make cutting easier. Methods of packaging integrated circuit devices using such conductive panels are also described.